reactjs - How to generate unique IDs for form labels in React?

Question

I have form elements with labels and I want to have unique IDs to link labels to elements with htmlFor attribute. Something like this:

React.createClass({
    render() {
        const id = ???;
        return (
            <label htmlFor={id}>My label</label>
            <input id={id} type="text"/>
        );
    }
});

I used to generate IDs based on this._rootNodeID but it’s unavailable since React 0.13. What is the best and/or simplest way to do it now?

Answer 1

The id should be placed inside of componentWillMount (update for 2018) constructor, not render. Putting it in render will re-generate new ids unnecessarily.

If you're using underscore or lodash, there is a uniqueId function, so your resulting code should be something like:

constructor(props) {
    super(props);
    this.id = _.uniqueId("prefix-");
}

render() { 
  const id = this.id;
  return (
    <div>
        <input id={id} type="checkbox" />
        <label htmlFor={id}>label</label>
    </div>
  );
}

2019 Hooks update:

import React, { useState } from 'react';
import _uniqueId from 'lodash/uniqueId';

const MyComponent = (props) => {
  // id will be set once when the component initially renders, but never again
  // (unless you assigned and called the second argument of the tuple)
  const [id] = useState(_uniqueId('prefix-'));
  return (
    <div>
      <input id={id} type="checkbox" />
      <label htmlFor={id}>label</label>
    </div>
  );
}